So I've done some searching and haven't found anything similar to what my G52 is doing so figured I'd ask here for some help.
The truck is an '85 Surf with a 2L diesel. After a week long trip of mixed driving in 35-40degC heat, including freeway driving, some low range work, some long steep climbs (20+mins of non-stop 2nd gear climbing) and driving through the mountains, it developed a noise on the drive home. I did have some overheating issues prior to the noise starting, temp up to 110degC max., then multiple instances of 100degC, where I'd have to pull over and let it cool down, so that may have something to do with the noise developing.
Basically it started making a noise that sounded like rocks in a tin can rattling. Pushing the clutch in had no effect, engine speed etc had no effect. So after some more driving around once I got it home, the noise was still present and started to get worse. It was in all gears (maybe only slightly in 4th). It would happen more often when slowing down prior to gearing down. Some slight clunking when first taking off.
So a few days ago I tried to recreate the noise and catch it on video. I set up a camera and drove past it a few times, of course, the noise disappeared. I stopped and reversed and did some short bursts of acceleration followed by slowing down to a roll. After doing this a few times, the noise has now disappeared. There was a slight whining when coasting but the rattling has stopped completely and has not returned after 3 days. There is a bit of vibration going on and a slight squealing when depressing the clutch pedal, but no rattle.
So after researching (I have minimal knowledge of gearboxes), I came to think that maybe it is a counter shaft bearing & pilot bearing or throwout bearing issue but would gladly welcome suggestions/information.
I have a lead on a few cheap R151F's, though just had my front driveshaft lengthened so not keen on swapping boxes if it means the driveshaft has to be changed. From what I can tell, if I get a R151F with the correct bellhousing, the only other thing I may need to do is open up the hole for the sticks and possibly change the crossmember, is that it?
Sorry if this has been covered before, I did try searching prior to posting.
